Spherical illuminator

ABSTRACT

A spherical illuminator (10, 40, 50, 60) having an upper diffuser (17, 47, 56, 62) with a concave surface, and having either an opposing reflector (18, 41) or an opposing lower diffuser (57, 63) with a concave surface. The two concave surfaces are placed so that their concavities form a substantially spherical viewing area into which the object under inspection is placed. The upper diffuser (10, 40, 50, 60) has a viewing aperture. It transmits light uniformly to the object from approximately two-pi steradians. The reflector (18, 41) or the lower diffuser (57, 63) provides light to the object in another two-pi steradians, resulting in nearly four-pi steradians of illumination.

TECHNICAL FIELD OF THE INVENTION

This invention relates to optical devices, and more particularly to anilluminator for a visual inspection system.

BACKGROUND OF THE INVENTION

Visual inspection systems can be designed for use by human inspectors orfor "machine vision" systems. In recent years, with the miniaturizationof electrical and electromechanical devices, a particular need hasarisen for inspection systems capable of detecting flaws in objectshaving very small features.

Most inspection systems include some sort of light source. Conventionallight sources include incandescent and fluorescent lamps and lightemitting diodes. Various optical arrangements have been designed forbetter illumination, such as ringed lamp arrays, focussed filamentprojectors, and fiber optic emitters. However, these conventionalilluminators tend to result in "hot spots" and other viewingdifficulties.

U.S. Pat. No. 5,051,872, entitled "Hemispherical Non-Glare Illuminator",assigned to Texas Instruments Incorporated, describes an illuminatorthat provides shadowless and uniform illumination. The illuminator has atranslucent hemispherical diffuser that is placed between a light sourceand the object to be viewed. The concavity of the diffuser is toward theobject to be viewed. The diffuser absorbs light incident on the convexsurface, and emits the light diffusely from the concave surface.

SUMMARY OF THE INVENTION

One aspect of the invention is a spherical illuminator for shadowlessillumination of an object under inspection. The illuminator has an upperdiffuser having a substantially hemispherical surface that is concavesuch that it forms an inner viewing area. This upper diffuser providestransmitted illumination from substantially all of the area of its innersurface, and has an aperture for permitting the object to be viewed fromoutside the upper diffuser. This upper diffuser provides two-pi ornearly two-pi steradians of illumination. The illuminator also haseither a reflector or a second diffuser. In either case, the reflectoror second diffuser has a substantially hemispherical surface thatopposes the concave surface of the upper diffuser. The reflector orsecond diffuser provides illumination from substantially all of the areaof its inner surface, and thereby provides another two-pi steradians ofillumination.

An advantage of the invention is that it provides nearly four-pisteradians of illumination. It eliminates hot spots and glare fromobjects that have shiny, specular, or otherwise highly reflectivefeatures. It also permits full inspection of objects that have irregularfeatures by avoiding shadows that would otherwise be caused by suchfeatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of an illuminator in accordance with theinvention, having an off-axis view port and a remote light source.

FIG. 2 is a perspective view of the illuminator of FIG. 1.

FIG. 3 illustrates the operation of an illuminator in accordance withthe invention.

FIG. 4 is a side sectional view of an alternative embodiment of theilluminator, which has an on-axis view port and an internal lightsource.

FIG. 5 is a side sectional view of an alternative embodiment of theilluminator, which has a second diffuser and light source, rather than areflector.

FIG. 6 is a side sectional view of an alternative embodiment of theilluminator, which has two solid diffusers.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 are a side sectional view and a perspective view,respectively, of a spherical illuminator 10 in accordance with theinvention. As explained below, illuminator 10 has a hemisphericaldiffuser 17 and a hemispherical reflector 18, which provide shadowlessillumination from "horizon-to-horizon" of an object under inspection(OUI).

The following description emphasizes those aspects of the invention thatinvolve reflector 18 and alternative embodiments thereof. Because ofreflector 18, illuminator 10 is a "spherical" as opposed to a"hemispherical" illuminator. Details of a hemispherical illuminator areset out in U.S. Pat. No. 5,051,872, entitled "Hemispherical Non-glareIlluminator", assigned to Texas Instruments Incorporated, andincorporated by reference herein.

Illuminator 10 has a housing 11 whose inner surface is reflective, atleast in part, consistent with the light path described below. Housing11 is at least substantially light-blocking except for a light port 12and a view port 13.

A fiber optic cable 15 provides the source illumination. Cable 15 entersilluminator 10 via light port 12. The light carried by cable 15 can begenerated by various means, but is typically generated by a lamp. Theradiation carried by cable 15 is not limited to visible light, and canbe ultraviolet or infrared. Light cable 15 terminates at light port 12.The light rays emitted from the termination end of cable 15 diverge dueto the aperture function.

Many variations for obtaining the source illumination are possible.Instead of being transmitted by a cable 15, light could be provided by alocal source at port 12. Also, as explained below in connection withFIG. 5, illuminator 10 could include an internal local source, such as afiber optic ring or an annular lamp.

The incoming light rays are incident upon a negative lens 16, whichcauses the rays to diverge so that they are incident on the uppersurface of a convex diffuser 17, as well as on the interior wall ofhousing 11 which is reflective where it surrounds the lower contour ofdiffuser 17. The angle of the wall of housing 11 and the cavitysurrounded by the housing are designed so that all of diffuser 17 isuniformly illuminated either by light rays directly from light port 12or after reflection from the wall of housing 11.

Diffuser 17 is a hollow hemisphere. Its diffusing characteristics can beinherent in the medium of diffuser 17 or can be provided by coating ortexturing either surface of diffuser 17. Examples of suitable materialfor diffuser 17 are milk glass, lexan, or polypropylene. The diffusivecharacteristic can be imparted by means such as sandblasting the surfaceof diffuser 17.

Diffuser 17 provides two-pi steradians of illumination, or nearly so,depending on various factors such as its diameter and the size of viewport 13. Diffuser 17 is referred to herein as the "upper" diffuser, todistinguish it from additional diffusers used in other embodiments.

Reflector 18 is also a hollow hemisphere. Reflector 18 is designated assuch because its concave surface is reflective. Reflector 18 is"opposing" with respect to diffuser 17 in the sense that its concavesurface is opposite the concave surface of diffuser 17 to form aspherical viewing area. In FIGS. 1 and 2, reflector 18 is approximatelythe same diameter as diffuser 17. However, this is not necessary, and insome cases, it may be desirable for reflector 18 to have a larger orsmaller diameter.

Reflector 18 has a diffusive surface, which can be accomplished byvarious means. For example, the inner surface of reflector 18 could becoated with a white film or paint. Or, reflector 18 could have whiteplastic surface that has been sandblasted to give it a diffusivecharacteristic.

Reflector 18 is detachable from housing 11, to permit the OUI to beinserted into the viewing area. A holding tool may be used to supportthe OUI within the viewing area. This tool may extend outside housing 11through a tool port 19. In the example of this description, the toolport 19 is at the junction where reflector 18 detaches from housing 11.The tool can be rotated, translated, or otherwise manipulated fordifferent views of the OUI.

View port 13 in housing 11 is aligned with an aperture 17a in diffuser17, so as to permit viewing of the OUI by the human eye or by devicessuch as a camera or a microscope. In FIGS. 1 and 2, view port 13 isoffset from an optical axis that is normal to the top of the OUI whenthe OUI is placed in the viewing area. This configuration of view port13 is an example of an "off-axis" configuration.

In FIGS. 1 and 2, illuminator 10 is oriented with respect to OUI, suchthat the diffuser 17 is the "upper" hemisphere and reflector 18 is the"lower" hemisphere. However, in other embodiments, these orientationscould be reversed, such that the view port is in reflector 18 ratherthan in diffuser 17.

FIG. 3 illustrates the operation of a spherical illuminator inaccordance with the invention. Only a view port 31 is explicitly shown.However, although not explicitly shown, the illuminator of FIG. 3 has adiffuser and reflector similar to those of FIGS. 1 and 2, as well as anaperture in the diffuser through which light may pass to view port 31.An OUI has been placed inside the illuminator, as shown in FIG. 1. InFIG. 3, the illuminator has an "on-axis" view port 31 as compared to the"off-axis" view port of FIGS. 1 and 2.

In the example of FIG. 3, the OUI is mound-shaped. Three points, P1, P2,and P3, on the OUI are illustrated. For simplicity, the eye of theviewer or the lens of the viewing device is assumed to be at the viewport 31. For each point, the light that must enter the eye or lens isillustrated in dotted lines. For each point, these light rays form a"solid angle" to the lens. For this "outgoing" light to be available,that point must be illuminated with light from within a specific solidangle of incident light. For point P1, this incident light arrives afterbeing transmitted through diffuser 17. However, for points P2 and P3,this incident light arrives after being reflected from reflector 18.

Point P2 is nearer to the horizontal line, H--H, upon which the OUIrests than is point P1. Point P3 is at the horizon. It is thus clearfrom FIG. 3, that illuminator provides horizon-to-horizon viewing of allpoints on the OUI. Expressed another way, the illuminator provides lightuniformly in a solid angle of four-pi steradians (360 degrees). Thereare no "dark zones" from which light does not reach the eye or lens.

FIG. 4 illustrates another illuminator 40, which has a reflector 41similar to reflector 18 of FIGS. 1 and 2. However, the view port 43 ofilluminator 40 is on-axis. A fiber optics cable 45 terminates at a lightring 46, which is an annulus of light emitting fibers. Light ring 46directs light rays to be incident on the surface of diffuser 47, whetherdirectly or after reflection from the inner surface of housing 48 orfrom reflectors 49.

FIG. 5 illustrates an alternative embodiment of the invention, referredto as an "active spherical illuminator" 50. In the embodiments of FIGS.1 and 2 and of FIG. 4, reflectors 18 and 41 are passive in the sensethat neither provides additional light. However, illuminator 50 has alower diffuser 57 instead of a reflector. Instead of reflecting lightinto the viewing area after that light has been transmitted through theupper diffuser 56, lower diffuser 57 itself transmits light into theviewing area. Lower diffuser 57 is substantially the counterpart ofupper diffuser 56, except that upper diffuser 56 has a viewing aperture56a in line with view port 51.

In FIG. 5, the light transmitted through upper diffuser 56 and lowerdiffuser 57 is obtained from a local source for each. In this example,illuminator 50 has two annular lamps 52 and 53. An upper housing 58 anda lower housing 59 have reflective inner walls so that light isuniformly transmitted by the entire surface of upper diffuser 56 andlower diffuser 57.

FIG. 6 illustrates another illuminator 60, which like illuminator 50 is"active". However, instead of having diffusers that are hollow spheres,illuminator 60 has two one-piece diffusers 62 and 63. Each diffuser 62and 63 feeds a spherical cavity 61, which acts as a diffuse lightradiator. This cavity's surface is treated to acquire a diffusingproperty. Like the reflectors and diffusers of other embodiments, theconical diffusers 62 and 63 are opposing.

Diffuser 62 has a view port 64. Both diffusers 62 and 63 have anassociated light ring 65 and 66, respectively, for illuminating thatdiffuser. Light enters the light rings 65 and 66 via fiber optic cables67 and 68.

The inner surfaces of diffusers 62 and 63 are angled to achieve internalreflection of light from the light rings 65 and 66, and especially todirect light to the areas of the diffusers that receive little or nolight directly. In this manner, the concave surfaces of diffusers 62 and63 are uniformly illuminated.

In each of the above embodiments of the spherical illuminator, thediffuser of the upper hemisphere and the reflector or diffuser of thelower hemisphere have been described as "substantially hemispherical".As this implies, either may be flattened to provide for a more compactilluminator without departure from the basic concept of the invention.

As is evident from the above-described embodiments, for both the upperdiffuser and for the lower diffuser, if there is a lower diffuser, manyvariations are possible with respect to the view port, light port, andlight source. For example, the light ring 53 configuration of FIG. 5could be used with an "off-axis" view port. Also, an "on-axis" view portcould be used with an "off-axis" fiber optic cable. Another alternativeis a local light source in the form of one or more annular lamps or aspiral neon lamp above the diffuser. Also, a beam splitter could beplaced over the aperture in the diffuser so as to avoid a dark spot.Further details about these variations are set out in U.S. Pat. No.5,051,872, referenced above.

Other Embodiments

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternative embodiments, will be apparent to persons skilled in the art.It is, therefore, contemplated that the appended claims will cover allmodifications that fall within the true scope of the invention.

What is claimed is:
 1. A spherical illuminator for shadowlessillumination of an object under inspection, comprising:a diffuser havinga substantially hemispherical surface that is concave such that saidsurface forms a cavity operable to act as a viewing area in which saidobject under inspection can be placed, said diffuser providingtransmitted illumination from substantially all of its concave surface;a reflector having a substantially hemispherical surface that is concaveand that opposes the concave surface of said diffuser, saidhemispherical surfaces of said reflector and said diffuser forming asphere, said reflector providing reflected illumination fromsubstantially all of the area of its concave surface; wherein saidilluminator has an aperture operable to permit said object underinspection in said cavity to be viewed.
 2. The illuminator of claim 1,wherein said diffuser is a hollow hemispherical shell having a diffusiveattribute.
 3. The illuminator of claim 2, further comprising a reflectoropposing at least an outer surface of said diffuser and directing lightfrom a source to said diffuser.
 4. The illuminator of claim 1, furthercomprising a light source providing light to be transmitted through saiddiffuser.
 5. The illuminator of claim 1, further comprising a housingsurrounding said diffuser.
 6. The illuminator of claim 5, wherein saidhousing has a light port receiving externally generated illumination.